Glycoprotein Synthesis in Plants

Abstract

Evidence is presented that enzymes present in crude extracts prepared from developing cotyledons of Phaseolus vulgaris can catalyze the transfer of radioactivity from UDP-N-[14C]acetylglucosamine into a chitobiosyl-lipid, lipid-oligosaccharide and glycoprotein. Kinetic evidence supports the concept that the N-acetylglucosamine-containing lipids are precursors to the glycoprotein. An interaction is shown between GDP-mannose and UDP-N-acetylglucosamine when used as substrates for the synthesis of lipid-oligosaccharide and glycoprotein. Kinetic evidence, as well as isolation and characterization of the oligosaccharides released from lipid by mild acid hydrolyses, support the conclusion that mannose and N-acetylglucosamine are contained in the same oligosaccharide and that N-acetylglucosamine is present at the reducing end of the oligosaccharide. Of the radioactivity which is incorporated from UDP-N-[14C]acetylguocosamine into the insoluble residue, 98% is solubilized by protease treatment. The glycopeptide released is quite similar in size and composition to the glycopeptide released by proteolytic digestion of vicillin, the major storage protein of P. vulgaris.